The HPE Aruba Networking AP-MNT-C mount bracket kit (R3J17A) is an individual Type C mounting accessory for a campus access point. It is made for a profile 9/16 suspended ceiling rail, providing the specified rail attachment for a compatible installation.
HPE lists the kit as compatible with the pre-assembled bracket on the AP-518. The mount kit is sold separately from that access point, so it is an accessory rather than part of the AP-518 package.